A typical vehicle air bag assembly comprises a folded air bag and an inflator which are disposed in a container. When the vehicle is involved in a collision, a crash sensor closes an electrical circuit to initiate operation of the inflator. The inflator discharges an inert gas (e.g., nitrogen) which forces the air bag out of the container and inflates the air bag. The air bag assembly is located in a vehicle so that the air bag, when forced out of the container, will cushion a vehicle occupant against impact with a structural part of the vehicle. One location for an air bag assembly is in the instrument panel or dashboard on the passenger side of the vehicle.
A known container construction for a passenger side air bag assembly comprises a reaction can with walls defining an internal cavity for storing a folded air bag and an inflator. The walls also define a deployment opening through which the air bag is directed when it is being inflated. A cover, or deployment door, covers the deployment opening to complete the container. The inflator and the folded air bag are located in the internal cavity and are coupled to respective portions of the reaction can. The cover is adapted to separate when pressure is applied to it. At the onset of a vehicle collision, the air bag is directed through the deployment opening, and applies pressure to the cover. The cover separates and enables the air bag to be forced out of the container and inflated in front of a vehicle occupant who is being pitched forward by the force of the collision.
During inflation of an air bag, the reaction can, which is generally made of metal (e.g., steel sheet), must withstand significant pressures. Specifically, a passenger side inflator, when actuated, is believed to produce gas pressure of approximately 30-50 psi in the reaction can. It has been found that under such pressure, portions of the walls forming the deployment opening of the reaction can may tend to bulge outward or "fishmouth" during deployment of the air bag. When the container is located just behind the vehicle instrument panel, fish-mouthing of the deployment opening of the reaction can may crack (or deform) the instrument panel. Such cracking or deformation may require replacement of the entire instrument panel.
One known technique for resisting fish-mouthing of an air bag reaction can is to bend outward certain portions of the metal walls forming the deployment opening of the reaction can. The walls are bent outward in the areas which are most prone to fish-mouthing. This technique increases the beam strength of those portions of the walls to resist fish-mouthing.
Another technique for resisting fish-mouthing of an air bag reaction can is disclosed in U.S. Pat. No. 4,842,300 to Ziomek, et al. In the Ziomek, et al. patent, a reaction member, preferably an inelastic fabric tether strap, extends across the deployment opening of the reaction can. At its ends, the tether strap is connected to the portions of the walls of the reaction can most prone to fish-mouthing. The tether strap restrains those portions of the walls of the reaction can from bulging outward under the pressures of air bag deployment.
Still other techniques for minimizing fishmouthing of the walls of an air bag receptacle are shown in co-pending application Ser. No. 07/629,427 entitled "Vehicle Air Bag Module and Method of Assembly", which is assigned to the assignee of the present invention. For example, as shown in the application, the reaction can may be specially formed with reinforcement components designed specifically to reinforce the portions of the deployment opening most prone to fishmouthing. Moreover, a continuous frame retainer is incorporated into the mouth of an air bag, for use in attaching the air bag to the reaction can. As explained in the application, the use of a continuous frame retainer provides a certain amount of inherent resistance to "fishmouthing" of the opening in the reaction can.
The preferred embodiment of the continuous frame retainer disclosed in co-pending application Ser. No. 07/629,427 has a substantially constant cross-sectional configuration. According to an alternative embodiment disclosed in the application, a selected portion of the continuous frame retainer has an additional flange. The additional flange adds beam strength to a portion of the reaction can, thereby increasing the deflection resistance of that portion of the reaction can. With a continuous frame retainer having the added beam strength, it is possible that the specially designed reinforcement components for the reaction can may be eliminated.